settings.outformat="pdf";
import graph;

real len=120,	ot=5,	alpha=120, beta=radians(alpha);
pair O=0,	A=O+(len,0),	B=O+(len*cos(beta), len*sin(beta));

draw( Arc( O, len,0,alpha ) );
draw( O--A ^^ O--B );
draw( O -- O+(ot,-ot) -- A-(ot,ot) -- A, gray);

